The existence of a nonadrenergic innervation of the respiratory system of man and animals has been demonstrated both by in vitro and in vivo techniques. However, the neurotransmitter for this innervation has not been conclusively identified. In this research plan two chemical agents (Vasoactive Intestinal Peptide - VIP; and Adenosine Triphosphate - ATP) will be evaluated for the transmitter role in the respiratory system of guinea pigs by physiological and radioimmunoassays. The tracheal pouch preparation, an in vivo physiologic technique designed to demonstrate the presence of the nonadrenergic innervation, will be used in the first project. By this method, the ability of VIP and ATP to produce a dose dependent relaxation will be determined by measuring the pressure decrease to graded doses in the isolated tracheal segment (pouch) of anesthetized guinea pigs. The responses of the pouch due to electrical stimulation of the nonadrenergic nerves (stimulation of the vagus after cholinergic and adrenergic blockade) will be measured along with radioimmunoassay of the tracheal pouch perfusate for the transmitter immediately after the nerve stimulation. Tachyphylaxis studies designed in this project will explore the possibility of receptor inactivation by continued exposure to the neurotransmitter by prolonged nerve stimulation as well as with continued incubation of the pouch with the exogenous potential neurotransmitters. In addition, the in vitro studies using tracheal spirals or parenchymal strips in the second part of the project will extend the investigation of the effect of these agents to the peripheral pulmonary tissues (parenchyma) for a better comparison with central airway (trachea). This study will also allow us to examine the effectiveness of these agents as possible inhibitory neurotransmitters in counteracting or inhibiting (partially or completely) the constrictor effects of histamine, a chemical mediator of anaphylaxis. The identification and characterization of the neurotransmitter of this inhibitory innervation may provide a new category of physiologic bronchodilators to the armamentarium for the treatment of hyperactivity of the airways, as in asthma.